This invention relates generally to hydrometallurgical separation of metal values from electrometallurgical anode slime and relates specifically to recovery of tin, lead, and precious metals from anode slime resulting in the electrolytic refining of secondary copper.
In the electrolytic refining of copper, electrolytic corrosion of impure copper anodes releases associated impurities. Those impurities which are more noble than copper do not dissolve in the electrolytic solution but rather settle to the bottom of the refining tank to form the anode slime which is periodically removed from the tank and treated to recover precious and other metals.
The composition of copper anode slime will generally vary according to the source of the copper, this variation being especially apparent as between primary sources and secondary sources. Even among secondary sources, there typically will be considerable variation in anode slime composition; however, such slimes are characterized by a large percentage of lead and tin content. A typical assay includes about 70% metal consisting of about 5 to 10% precious metals, 25% tin, and 50% lead with the balance being composed of various other metals. For purposes herein, the term "precious metals" (PM's) refers primarily to platinum, palladium, gold, and silver.
There is substantial economic incentive for separating tin from the slimes, in addition to PM's, considering the relatively large portion of tin making up the slimes and the unit market value of tin, the tin value being a significant percentage of the PM value per unit weight of slimes. Apparently, conventional methods for concentrating PM's from starting materials similar to copper anode slimes either do not separate a tin concentrate or, if so, involve substantial use of energy-intensive pyrometallurgical processes to separate lead and tin. Thus, the present invention is concerned with treatment of anode slimes by energy-conservative hydrometallurgical processes to concentrate tin, as well as PM's.
Of particular interest in the present invention concerning the removal of lead is the process disclosed in U.S. Pat. No. 2,950,964 issued Aug. 30, 1960 to F. Forward et al, hereby incorporated by reference. The process concentrates lead by selective dissolution of oxidized lead compounds, especially lead sulfate, in an alkylene amine aqueous solution.
Of general interest concerning concentration of PM's are ion exchange techniques, such as is briefly described in British Pat. No. 1,418,391 issued Dec. 17, 1975, hereby incorporated by reference, wherein platinum-group metals and gold are leached from the ore with an acid and an oxidizing agent, then the loaded leach solution is contacted with an exchange resin selective to adsorption of such PM's followed by elutriation of the loaded resin with thiourea, and finally extracting the PM's from the loaded eluate by liquid-liquid extraction.
The present invention advantageously utilizes the appropriate features of these processes as components in an overall process for the hydrometallurgical treatment of copper anode slimes to separate approximately 85% of the metal value contained therein, including tin as well as PM's.